1. Field of the Invention
The present invention relates to a ceramic granule for molding a ceramic product, a process for producing the same or a process for treating the same, a ceramic product obtained therefrom, and a process for producing the ceramic product. More specifically, the present invention relates to a ceramic granule excelling in a molding property, a process for producing or treating the same, a ceramic product having a high dimensional accuracy, and a process for producing the ceramic product.
2. Description of the Related Art
From the viewpoints of a relatively simple manner, a low cost, and the capability of producing a ceramic product on a large scale, a dry pressure molding has been utilized as one process for producing a ceramic product. When a ceramic product is produced by this process, it is general to granulize ceramic particles into ceramic granules for the purpose of easy transportability of the powder, operability in packaging and molding, etc.
As a process for granulating ceramic particles, there are two popular processes: (1) a process (spray drying process) in which an aqueous slurry comprising a ceramic material, a binder, and water is spray-dried by means of a spray dryer to produce a ceramic granule, and (2) a process (oscillating extruding process) in which ceramic particles are granulated into ceramic granules by repeating drying and oscillating extruding have been utilized.
The spray-drying process which can easily control the particle distribution is suitable for producing a large amount of ceramic granules having a relatively small particle diameter. On the other hand, the oscillating extruding process which can be easily operated is suitable for producing relatively compact granules in a small scale plant. The granulation is appropriately selected from these processes depending upon a molded product to be produced, a mold to be used, a production scale, and the like.
In order to produce a ceramic molded product, the ceramic granules are required to possess the following characteristics:
(1) The ceramic granules should have flowability within a suitable range, and a good packing property during the course of packing the ceramic granules into a mold in a uniform manner.
(2) The ceramic granules should be crushed at a low pressure (typically from 0.3 to 1.5 ton/cm2) during the course molding (hereinafter referred to as xe2x80x9ca crushing property at a low pressurexe2x80x9d).
(3) Ingredients such as fine particles contained in the ceramic granule should not be stuck to a mold or the like (hereinafter referred to as xe2x80x9canti-sticking propertiesxe2x80x9d).
(4) The ceramic granules are not collapsed during the course of the storage, transportation, agitation when they are packed into a mold, or due to collision with each other (hereinafter referred to as xe2x80x9can anti-collapse propertyxe2x80x9d).
(5) The ceramic granules have suitably bulk density so that they flow out of the mold during the course of packing them into a mold, or of molding (hereinafter referred to as xe2x80x9ca mold-packing propertyxe2x80x9d).
Particularly, the ceramic particles are required to possess conflicting characteristics, i.e., xe2x80x9cthe crushing property at a low pressurexe2x80x9d and xe2x80x9cthe anti-collapse propertyxe2x80x9d.
Various processes have been suggested in order to satisfy these requirements. For example, Japanese unexamined Patent Publication No. 5-159918 and Japanese examined Patent Publication No. 7-17460 disclose processes for improving the flowability and the crushing property at a low pressure utilizing specific dispersants in the preparation of an aqueous slurry.
Japanese examined Patent Publication No. 3-31660 and Japanese unexamined Patent Publication No. 10-59776 disclose processes for improving the flowability and the crushing property at a low pressure of the ceramic granules by decreasing the segregation of the binder.
According to these processes, it is disclosed that ceramic granules having improved flowability, relatively a good mold-packing property, and a crushing property at a low pressure of the ceramic granules can be obtained.
However, these techniques have the following drawbacks:
(1) Since these techniques concern the improvement of aqueous slurry, the granulation process is restricted to the spray-drying process using a spray dryer, leading to poor popularization.
(2) Although the flowability and the crushing property at a low pressure of the ceramic granules are somewhat improved, the something to further improved has been still left. Also, the molded product produced by the use of such ceramic granules has insufficient dimensional accuracy. Further, these ceramic granules are not suitable for producing a ceramic product having a complicated shape.
(3) The ceramic granules are sometimes collapsed during the course of the storage, transportation, or packing them into a mold.
(4) When being molded in a mold, the fine ceramic particles are stuck to the mold, causing sticking, which in some cases makes it impossible to continuously produce ceramic products.
(5) In the ceramic granule granulated by these techniques, due to the storage over a prolonged period of time or distillation of the water, the binder is segregated, cured, or partially converted into fine particles. This changes the properties at the time of the production, such as the flowability, the crushing property at a low pressure of the ceramic granules, or the anti-sticking property.
Consequently, a first object of the present invention is to provide a ceramic granule excelling in the flowability, the mold-packing property, and the anti-sticking property, and having a well-balanced properties of conflicting properties of the crushing property at a low pressure and the anti-collapse property, and capable of continuously producing a ceramic product.
A second object of the present invention is to provide a process for producing such a ceramic granule in a stable manner.
A third object of the present invention is to provide a process for treating a ceramic granule whose required properties have been deteriorated with the elapse of the time to be activated or an existing ceramic granule to impart such properties.
A fourth object of the present invention is to provide a ceramic product having a high dimensional accuracy.
A fifth object of the present invention is to provide a process for producing a ceramic product having a high dimensional accuracy from a ceramic granule excelling in the flowability, the mold-packing property, and the crushing property at a low pressure, and having a little sticking fine particle to a mold.
As a result of our studies and researches in light of the above circumferences, it has been found that when a ceramic granule is moistened under specific conditions by a specific manner, the above objects can be attained to complete the present invention.
The present invention concerns the following first to fifth aspects:
1. A ceramic granule for producing a ceramic product comprising at least one ceramic particle and a binder, said ceramic granule is moistened under the conditions that the water content of the surface of the ceramic granule is within the range sufficient for maintaining the flowability for packing the ceramic granule into a mold, and the total water content of the ceramic granule is within the range that a crushing property at a low temperature and an anti-collapse property of the ceramic granule are well balanced.
2. A ceramic granule for producing a ceramic product comprising at least one ceramic particle and a binder, the total water content of the ceramic granule ranging from 0.1 to 6.0% by weight, the internal water content of the ceramic granule which occupies xc2xe of the total granule ranging from 0.1 to 7.3% by weight, and the external water content of the ceramic granule which occupies xc2xc of the total granule ranging from 0 to 2.0% by weight.
3. The ceramic granule as described in (1) or (2) above, wherein the moistening of the ceramic granule is carried out within an agitation fluidized bed.
4. The ceramic granule as described in one of (1) to (3) above, wherein the ceramic granule is granulated by spray drying and the surface of the granule is compact.
5. The ceramic granule as described in one of (1) to (3) above, wherein the ceramic granule is granulated by oscillating extruding process.
6. The ceramic granule as described in one of (1) to (5) above, wherein fine particle having a particle size not more than 10 xcexcm has been removed by classification.
7. The ceramic granule as described in one of (1) to (6) above, wherein the particle size of the ceramic particles has been regulated.
8. The ceramic granule as described in one of (1) to (7) above, wherein said ceramic granule comprises ferrite particle.
9. A process for producing a ceramic granule for producing a ceramic product which comprises the following steps:
a step for granulating one or more ceramic particle into a granule together with a binder;
a step for moistening the granulated ceramic in an agitation fluidized bed under the conditions of not aggregating said ceramic granule;
a step for regulating the water content of the moistened ceramic granule by fluidizing and drying the water-added ceramic in the agitation fluidized bed in such a manner that the resultant granule has a water content within the range which maintains a flowability sufficient for packing the ceramic granule in a mold for producing a ceramic product and in which the ceramic granule exhibits well-balanced properties of a crushing property at a low pressure and an anti-collapse property; and
a step for regulating the particle size of the ceramic granule.
10. The process as described in (9) above, which further comprises: a step for carrying out classifying in the agitation fluidized bed by means of a bag filter or air-classification to remove fine particles having a particle size of not more than 10 xcexcm, after the step for granulating one or more ceramic particle into a granule together with a binder.
11. The process as described in (9) or (10) above, wherein the moistening is carried out so that the total water content of the ceramic granule ranging from 0.1 to 6.0% by weight, the internal water content of the ceramic granule which occupies xc2xe of the total granule ranging from 0.1 to 7.3% by weight, and the external water content of the ceramic granule which occupies xc2xc of the total granule ranging from 0 to 2.0% by weight.
12. The process as described in any one of (9) to (11) above, wherein the temperature of the agitation fluidized bed is set to the range from 20 to 50xc2x0 C. by supplying hot air of 50 to 80xc2x0 C. to the agitation fluidized bed.
13. The process as described in any one of (9) to (12) above, wherein the ceramic granule is granulated by a spray-drying process.
14. The process as described in (13) above, wherein the ceramic granule is granulated in the agitation fluidized bed.
15. The process as described in any one of (9) to (12) above, wherein the ceramic granule is granulated by an oscillating extruding.
16. A process for treating a ceramic granule, which comprises the following steps:
a step for incorporating a ceramic granule obtained by granulating one or more ceramic particle into a granule together with a binder in an agitation fluidized bed, and moistening the granulated ceramic under the conditions of not aggregating said ceramic granule;
a step for regulating the water content of the moistened ceramic granule by fluidizing and drying the water-added ceramic in the agitation fluidized bed in such a manner that the resultant granule has a water content within the range which maintains a flowability sufficient for packing the ceramic granule in a mold for producing a ceramic product and in which the ceramic granule exhibits well-balanced properties of a crushing property at a low pressure and an anti-collapse property; and
a step for classifying the moistened ceramic granule.
17. The process as described in (16) above, which further comprises: a step for carrying out classifying in the agitation fluidized bed by means of a bag filter or air-classification to remove fine particles having a particle size of not more than 10 xcexcm, after the step for granulating one or more ceramic particle into a granule together with a binder.
18. The process as described in (16) or (17) above, wherein the moistening is carried out so that the total water content of the ceramic granule ranging from 0.1 to 6.0% by weight, the internal water content of the ceramic granule which occupies xc2xe of the total granule ranging from 0.1 to 7.3% by weight, and the external water content of the ceramic granule which occupies xc2xc of the total granule ranging from 0 to 2.0% by weight.
19. The process as described in any one of (16) to (18) above, wherein the temperature of the agitation fluidized bed is set to the range from 20 to 50xc2x0 C. by supplying hot air of 50 to 80xc2x0 C. to the agitation fluidized bed.
20. A ceramic product having a high accuracy obtained by molding the ceramic granule described in anyone of (1) to (8) above into a ceramic product.
21. A process for Producing Ceramic Product, which comprises the following steps:
a step for incorporating a ceramic granule obtained by granulating one or more ceramic particle into a granule together with a binder in an agitation fluidized bed, and moistening the granulated ceramic under the conditions of not aggregating said ceramic granule;
a step for regulating the water content of the moistened ceramic granule by fluidizing and drying the water-added ceramic in the agitation fluidized bed in such a manner that the resultant granule has a water content within the range which maintains a flowability sufficient for packing the ceramic granule in a mold for producing a ceramic product and in which the ceramic granule exhibits well-balanced properties of a crushing property at a low pressure and an anti-collapse property;
a step for regulating the particle size of the ceramic granule; and
a step for molding the resulting ceramic granule into a ceramic product.
22. The process as described in (21) above, which further comprises: a step for carrying out classifying in the agitation fluidized bed by means of a bag filter or air-classification to remove fine particles having a particle size of not more than 10 xcexcm, after the step for granulating one or more ceramic particle into a granule together with a binder.
23. The process as described in (21) or (22) above, wherein the moistening is carried out so that the total water content of the ceramic granule ranging from 0.1 to 6.0% by weight, the internal water content of the ceramic granule which occupies xc2xe of the total granule ranging from 0.1 to 7.3% by weight, and the external water content of the ceramic granule which occupies xc2xc of the total granule ranging from 0 to 2.0% by weight.
24. The process as described in any one of (21) to (23) above, wherein the temperature of the agitation fluidized bed is set to the range from 20 to 50xc2x0 C. by supplying hot air of 50 to 80xc2x0 C. to the agitation fluidized bed.
25. The process as described in any one of (21) to (23) above, wherein the ceramic granule is granulated by a spray drying process.
26. The process as described in anyone of (21) to (23) above, wherein the ceramic granule is granulated by an oscillating extruding.